The invention concerns an ignition system.
Electronic components in the motor vehicle, and in particular in the engine compartment, must meet special demands. On the one hand, the semiconductor components must tolerate high temperatures and, on the other hand, the components must meet extremely high demands if the high voltage necessary for the ignition is applied directly to the semiconductor components. In order to accept the high voltages, several semiconductor components must be connected in series. This is expensive and involved. Still, a destruction of the components through excess voltages cannot be ruled out with certainty.
An ignition distributor arrangement is known from DE 37 22 666 A1, where the ignition pulses supplied by the ignition coil are fed by way of semiconductor components to the spark plug. The semiconductor components in this case are switched by exposing them to light.
Field emitters are known, among other things, from publications by C. Spindt, Stanbord Research Institute. So far, they have primarily been used for displays.
The field emitter, a vacuum microelectronic component, utilizes the controlled emission of electrons from a metal tip or edge into the vacuum. FIG. 1 shows the basic configuration of a vertical field emitter with field-emission cathode and the tunnel effect. The metal tip is located in a high electrical field at room temperature.
As a result of the metal tip shape, field strength magnifications up to the range of several 10 .sup.7 V/cm are possible. These field strengths are sufficient for permitting electrons to tunnel through the potential barrier at the work function level. Owing to the small distance between cathode tip and edge of the gate hole and the considerably larger distance to the anode for voltages of the same order of magnitude on both electrodes, it is essentially the gate voltage that determines the field strength prevailing for the field emission at the cathode.
After leaving the tip, the electrons are accelerated near the cathode already to a noticeable amount of the final speed, in contrast to the emission from thermal cathodes. Their movement direction is essentially determined by the angle of emission, as long as the anode voltage is higher than the gate voltage. If the anode voltage is lower than the gate voltage, then the electrons are decelerated near the anode. Some electrons (with a high angle to the rotational axis of the tip) reverse their movement direction and move toward the gate. The remaining electrons reach the anode. Some of them are reflected by the anode and also move toward the gate. Since the electron movement speeds near the anode are very low, it is possible for space charges to form at high currents, which increase the decelerating electrical field.
In-depth studies of the space charges are still the subject matter of research. An anode and a gate current are flowing. In addition to the voltage ratio at the anode and the gate, the current ratio depends in a complex way on the geometric arrangement.